Ahead of today's opening free practice session, the air temperature is 25 degrees C while the track temperature is 28 degrees. Surprisingly, it is somewhat overcast.

Having originally intended to use its medium (prime) and supersoft (option) tyres, Pirelli is instead running medium and soft - the harder compound making its 2011 debut after a successful test in Canada two weeks ago.

As in Montreal there are two DRS zones, one beginning on the approach to Turn 11 - the only straight of substance here - and the other coming out of Turn 14 and the run to Turn 17. The DRS detection zone is on the approach to Turn 8.

While a number of teams have brought updates here, even Hispania, the main talking point is the new rule regarding changes to engine mapping between qualifying and the race. It is this rule - together with the ban on blown diffusers from Silverstone onwards - that is expected to tighten up the field though Red Bull remains extremely confident that it will be business as usual.

Nico Hulkenberg is in Paul di Resta's car this morning while Daniel Ricciardo is in for Sebastien Buemi and Karin Chandhok for Jarno Trulli. Sergio Perez, has said that he will make a decision on the remainder of the weekend after today's two sessions - the Mexican having withdrawn from the Canadian Grand Prix weekend after the Friday morning session.

The lights go green and, surprisingly, Sebastian Vettel is the first driver out, followed by Hulkenberg, Alguersuari, Petrov and Ricciardo. From the outset it is noticeable how dusty it is here.

Six minutes into the session all but Schumacher, Heidfeld and the McLaren duo have been out.

While the rest complete an installation lap before diving back into the pits, Rosberg stays out to post the first time of the day, the German crossing the line at 2:06.412.

Fifteen minutes into the session, with all drivers now having completed an installation lap, Hulkenberg posts a 1:47.942. In the McLaren garage crew members are clearly unhappy when the camera closes in on the team's new rear wing. The Woking outfit is also running a new front wing.

As Hulkenberg improves to 46.302, fellow countryman Schumacher posts a 54.397. Moments later the Force India posts a 44.929.

In the Red Bull garage Vettel looks pensive as he chats with Helmut Marko, the media still speculating as to how he'll recover following his Montreal mistake.

Hulkenberg loses the rear end of the Force India under braking for Turn 12, the German clouting the wall and bringing out the yellow flags.

Fresh from his success in Canada, Alguersuari goes second with a 44.358 as Maldonado posts 45.381 to go third.

Having gone quickest in all three sectors, Maldonado takes the top spot with a 43.455, though, after thirty-one minutes, only six drivers have posted times.

Schumacher improves to fourth with a 44.213 as Massa heads down the pitlane, followed, shortly after, by teammate Alonso.

A 43.050 sees Schumacher go quickest, while Ricciardo goes second ahead of Maldonado, Sutil, Alguersuari and Heidfeld.

Massa posts a 42.530 to take the top spot while Alonso goes seventh (43.622), however, next time around the Spaniard goes quickest (41.683) to make it a Ferrari 1-2.

As Hamilton explains that his rear wing isn't engaging, he is told that his DRS has been disabled. Elsewhere, Chandhok is running very slowly in the Lotus, the Indian being told to use high gears and definitely not to use second.

At half-time, it's: Alonso, Sutil, Massa, Button, Heidfeld, Rosberg, Petrov, Schumacher, Hamilton and Barrichello. All but Vettel, d'Ambrosio, Kovalainen, Kobayashi and Chandhok have posted times.

Webber improves from fifteenth to sixth with a 42.486 as Chandhok confirms that his session is over his Friday jinx striking yet again. A couple of laps later, Webber improves to second with a 41.285.

Vettel goes seventeenth with a 43.860 as the cameras pick up Kobayashi running wide.

Webber goes quickest (40.852) having gone quickest in S3, while Schumacher emulates Kobayashi's off.